[LTP] [PATCH v2] mmap04.c: Avoid vma merging

[Martin Doucha]

Hi,
Reviewed-by: Martin Doucha <mdoucha@suse.cz>

On 24. 01. 24 14:26, Avinesh Kumar wrote:
> We hit a scenario where new mapping was merged with existing mapping of
> same permission and the return address from the mmap was hidden in the
> merged mapping in /proc/self/maps, causing the test to fail.
> To avoid this, we first  create a 2-page mapping with the different
> permissions, and then remap the 2nd page with the perms being tested.
> 
> Signed-off-by: Avinesh Kumar <akumar@suse.de>
> Reported-by: Martin Doucha <mdoucha@suse.cz>
> Signed-off-by: Avinesh Kumar <akumar@suse.de>
> ---
>   testcases/kernel/syscalls/mmap/mmap04.c | 23 ++++++++++++++++-------
>   1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/testcases/kernel/syscalls/mmap/mmap04.c b/testcases/kernel/syscalls/mmap/mmap04.c
> index f6f4f7c98..fa85deed1 100644
> --- a/testcases/kernel/syscalls/mmap/mmap04.c
> +++ b/testcases/kernel/syscalls/mmap/mmap04.c
> @@ -17,8 +17,8 @@
>   #include "tst_test.h"
>   #include <stdio.h>
>   
> -#define MMAPSIZE 1024
> -static char *addr;
> +static char *addr1;
> +static char *addr2;
>   
>   static struct tcase {
>   	int prot;
> @@ -44,14 +44,23 @@ static struct tcase {
>   static void run(unsigned int i)
>   {
>   	struct tcase *tc = &tcases[i];
> -	char addr_str[20];
>   	char perms[8];
>   	char fmt[1024];
> +	unsigned int pagesize;
> +	int flag;
>   
> -	addr = SAFE_MMAP(NULL, MMAPSIZE, tc->prot, tc->flags, -1, 0);
> +	pagesize = SAFE_SYSCONF(_SC_PAGESIZE);
>   
> -	sprintf(addr_str, "%" PRIxPTR, (uintptr_t)addr);
> -	sprintf(fmt, "%s-%%*x %%s", addr_str);
> +	/* To avoid new mapping getting merged with existing mappings, we first
> +	 * create a 2-page mapping with the different permissions, and then remap
> +	 * the 2nd page with the perms being tested.
> +	 */
> +	flag = (tc->flags & MAP_PRIVATE) ? MAP_SHARED : MAP_PRIVATE;
> +	addr1 = SAFE_MMAP(NULL, pagesize * 2, PROT_NONE, MAP_ANONYMOUS | flag, -1, 0);
> +
> +	addr2 = SAFE_MMAP(addr1 + pagesize, pagesize, tc->prot, tc->flags | MAP_FIXED, -1, 0);
> +
> +	sprintf(fmt, "%" PRIxPTR "-%%*x %%s", (uintptr_t)addr2);
>   	SAFE_FILE_LINES_SCANF("/proc/self/maps", fmt, perms);
>   
>   	if (!strcmp(perms, tc->exp_perms)) {
> @@ -61,7 +70,7 @@ static void run(unsigned int i)
>   						tc->exp_perms, perms);
>   	}
>   
> -	SAFE_MUNMAP(addr, MMAPSIZE);
> +	SAFE_MUNMAP(addr1, pagesize * 2);
>   }
>   
>   static struct tst_test test = {

-- 
Martin Doucha   mdoucha@suse.cz
SW Quality Engineer
SUSE LINUX, s.r.o.
CORSO IIa
Krizikova 148/34
186 00 Prague 8
Czech Republic